The invention is directed to an aqueous treatment composition and a method for rendering porous substrates water repellent and for preserving porous substrates utilizing the aqueous treatment composition.
Generally, the art-known porous substrate treatment compositions such as wood treatment compositions are organic solvent-borne compositions. For example, U.S. Pat. Nos. 4,360,385 and 4,404,239 are directed to solvent-borne wood treatment compositions containing olefin and paraffin materials containing a substantial proportion of compounds containing from about 20 to 24 carbon atoms and, optionally, additives such as wood preservatives, alkyd resins and organic ionizable compounds. It is disclosed in the aforesaid United States patents that such art-known organic solvent-borne wood treatment compositions can provide wood with water-repellency at an efficiency level of at least about 40 percent, preferably at least about 50 percent and more preferably at least about 60 percent as determined by the N.W.M.A. Swellometer Test described in detail in a publication identified as NWMA-M-2-81, published by the National Woodwork Manufactures Association.
Increasing environmental concerns have generated an ever increasing need to develop treatment compositions with lower levels of organic solvents. One approach to reducing the organic solvent content investigated by the present inventors involves the utilization of an aqueous treatment composition. However, heretofore water-borne wood treatment compositions have not been able to provide nearly the level of water-repellency to wood as organic solvent-borne treatment compositions. For example, N.W.M.A. Swellometer Test NWMA-M-2-81, Sec. 3.2.1 concerning the method of treating wood for the purposes of the test discloses that the five test specimens (immersed) in the formulation to be tested have an immersion time for solvent-based formulations of 30 seconds and immersion time for water-borne formulations of 3 minutes. In part, the difficulty in water-repellency is believed to be due to the inefficient penetration of the wood by the water-borne formulation. Penetration of wood by water is inefficient because water, upon penetrating wood, swells the wood and hinders further penetration of the wood. Hence, other ingredients are hindered from penetrating the wood in a short exposure time. By the present invention, there is provided an aqueous wood-treating composition having penetration and water-repellency that is comparable to that of solvent-borne compositions.
U.S. Pat. No. 4,612,255 (Hein) discloses water dispersible wood treatment compositions. However, the compositions still include substantial amounts of organic solvent (the zinc-containing preservatives employed contain about 44% mineral spirits), such that the volatile organic content is greater than desired. In the examples set forth in that patent the V.O.C. ranges from 3.72 to 4.06. It would be desirable for the V.O.C. to be less than 3.5, preferably less than 3.0. It may also be noted that the water reducible concentrates in the Hein patent are totally organic compositions, not waterborne dispersions. Thus, Hein relies upon substantial amounts of surfactant to permit reduction with water, and high levels of surfactant can detrimentally affect penetration of treatment solutions into wood. It appears that penetrability of Hein's compositions rely upon the relatively large amounts of organic solvents that are included.